Speaking as someone in the game industry, Valve certainly has it's problems, but they aren't platform problems.
PC is stronger this generation than it was last generation, I'm not sure about the numbers but I suspect that it is ahead of both consoles, and it might be ahead of both of them combined, and I'd expect this to only be get more true. Porting to PC is pretty much just porting the parts that interact with the OS or GPU for this generation, due to both consoles using x86-64.
And mobile is a joke. market might be huge, there's a reason very few established game companies care about it at all. It's extremely unpredictable, and the expected price of games is far below what is realistic. Even if you make a hit, the amount of money you'll make is far from the amount of money you make from a hit on any other platform (hell, it doesn't even come close to the budget of most games). Honestly, I think the only way a company can hope to turn a profit on mobile is with IAP or shovelware (or both), and I don't see that displacing console or PC gaming any time soon.
I wouldn't mind seeing steam displaced, but I don't think it will be by EA or Ubisoft, largely due to the fact that they're both about as popular as Comcast, which seems to be due to them being massively out of touch.